1. Field of the Invention
The present invention relates to dimerizing, co-dimerizing or oligomerizing and also polymerizing olefins. More particularly, it relates to a catalyst composition for catalyzing the reactions occurring in those processes.
α-linear olefins, in particular those containing 4 to 10 carbon atoms, used as co-monomers for producing low density polyethylene (LLDPE) or as intermediates in producing detergents or lubricants, are becoming more important commercially. The majority of industrial processes for producing α-olefins are processes for oligomerizing ethylene catalyzed by transition metal complexes (Ni, Ti, Zr) or AlEt3 (Alpha Olefins Applications Handbook, G. R. Lapin and J. D. Sauer, Eds, M. Dekker, N.Y., 1989). The majority of those processes result in broad distributions of α-olefins: C4 to C20+.
2. Description of the Prior Art
We are constantly researching novel catalytic systems that can produce narrower olefin distributions, for example to optimize the formation of C4-C10, and which are more selective for linear α-olefins and more active.
It has recently been demonstrated (S Svejda et al, Organometallics, 1999, 18, 65-74; International Patent applications WO 96/02310; WO 00/10945; U.S. Pat. No. 5,880,323) that systems comprising a nickel complex in combination with nitrogen-containing ligands of the α-type diimine in the presence of a Lewis acid or a Brønsted acid, and more particularly an aluminum derivative such as an aluminoxane or an alkyl aluminum chloride, can catalyze the oligomerization of ethylene to linear α-olefins. However, in such systems, large quantities of aluminoxane are generally used (more than 100 equivalents per mole of nickel) and the distribution of the olefins formed is generally wide: C4 to C20, with a Schulz-Flory constant of more than 0.6.
Further, neutral nickel complexes comprising chelated P—O type ligands have been used for more than 20 years as precursors in the “SHOP” process from Shell for the oligomerization of ethylene to C4-C20+ linear α-olefins. The particular feature of that process is that the nickel complex is dissolved in a polar diol type solvent such as 1,4-butanediol, in which the reaction products are only slightly miscible. This two-phase operation enables the products to be separated by decanting and allows the catalyst to be recycled.
French Patent No. 2,611,700 describes the use of liquids with an ionic nature formed from aluminum halides and quaternary ammonium halides as solvents for organometallic nickel complexes for catalyzing olefin dimerization. The use of such media which are not miscible with aliphatic hydrocarbons, in particular with olefin dimerization products, allows better use of homogeneous catalysts. Further, such media can be used with organometallic complexes, which are reactive in the presence of protic compounds such as the diols described in the “SHOP” process.
U.S. Pat. No. 5,104,840 describes a liquid composition with an ionic nature resulting from contacting quaternary ammonium halides and/or quaternary phosphonium halides with alkyl aluminum dihalides and an optional aluminum trihalide. That patent also describes the use of such media as solvents for transition metal complexes, in particular nickel complexes containing no nickel-carbon bond, which are transformed into catalysts for oligomerizing olefins.